Symmetry | Group actions (mathematics) | Representation theory of groups | Group theory
In mathematics, a group action on a space is a group homomorphism of a given group into the group of transformations of the space. Similarly, a group action on a mathematical structure is a group homomorphism of a group into the automorphism group of the structure. It is said that the group acts on the space or structure. If a group acts on a structure, it will usually also act on objects built from that structure. For example, the group of Euclidean isometries acts on Euclidean space and also on the figures drawn in it. For example, it acts on the set of all triangles. Similarly, the group of symmetries of a polyhedron acts on the vertices, the edges, and the faces of the polyhedron. A group action on a vector space is called a representation of the group. In the case of a finite-dimensional vector space, it allows one to identify many groups with subgroups of GL(n, K), the group of the invertible matrices of dimension n over a field K. The symmetric group Sn acts on any set with n elements by permuting the elements of the set. Although the group of all permutations of a set depends formally on the set, the concept of group action allows one to consider a single group for studying the permutations of all sets with the same cardinality. (Wikipedia).
Group actions in abstract algebra
In this first video on group actions, I use an example of some previous work on the symmetric group to give you some intuition about group actions. Beware when reading your textbook. It is probably unnecessary difficult just due to the dot notation that is used when describing group acti
From playlist Abstract algebra
What is a Group Action? : A Group as a Category and The Skeleton Operation ☠
This week I try to take a more Categorical approach to answering and expanding upon the question of "what is a group action". Along the way I'll go over thinking about a group as a category and eventually hit on the skeleton operation on a category and use it to present an example of the c
From playlist The New CHALKboard
In this video I demonstrate an example of a non-faithful group actions, where the identity permutation is actually mapped to by all the elements in the group set. Another example shows you how group actions involving a group set on itself gives rise to group element composition as we see
From playlist Abstract algebra
Abstract Algebra: Group actions are defined as a formal mechanism that describes symmetries of a set X. A given group action defines an equivalence relation, which in turn yields a partition of X into orbits. Orbits are also described as cosets of the group. U.Reddit course materials a
From playlist Abstract Algebra
Definition of a group Lesson 24
In this video we take our first look at the definition of a group. It is basically a set of elements and the operation defined on them. If this set of elements and the operation defined on them obey the properties of closure and associativity, and if one of the elements is the identity el
From playlist Abstract algebra
Visual Group Theory, Lecture 5.1: Groups acting on sets
Visual Group Theory, Lecture 5.1: Groups acting on sets When we first learned about groups as collections of actions, there was a subtle but important difference between actions and configurations. This is the tip of the iceberg of a more general and powerful concept of a group action. Ma
From playlist Visual Group Theory
Group action proofs in abstract algebra
This video follows from the previous one, in which we developed an intuitive understanding of group actions by way of an example. In this video I want to spend a few minutes on the proofs that connect the elements in a group set with the permutations of another set.
From playlist Abstract algebra
Visual Group Theory, Lecture 5.3: Examples of group actions
Visual Group Theory, Lecture 5.3: Examples of group actions It is frequently of interest to analyze the action of a group on its elements (by multiplication), subgroups (by multiplication, or by conjugation), or cosets (by multiplication). We look at all of these, and analyze the orbits,
From playlist Visual Group Theory
A group is (in a sense) the simplest structure in which we can do the familiar tasks associated with "algebra." First, in this video, we review the definition of a group.
From playlist Modern Algebra - Chapter 15 (groups)
Denis Osin: Acylindrically hyperbolic groups (part 1)
The lecture was held within the framework of Follow-up Workshop TP Rigidity. 28.4.2015
From playlist HIM Lectures 2015
Rigidity for von Neumann algebras – Adrian Ioana – ICM2018
Analysis and Operator Algebras Invited Lecture 8.5 Rigidity for von Neumann algebras Adrian Ioana Abstract: We survey some of the progress made recently in the classification of von Neumann algebras arising from countable groups and their measure preserving actions on probability spaces.
From playlist Analysis & Operator Algebras
Euler's formula with introductory group theory
Intuition for e^(πi) = -1, using the main ideas from group theory Help fund future projects: https://www.patreon.com/3blue1brown An equally valuable form of support is to simply share some of the videos. Special thanks to these supporters: http://3b1b.co/epii-thanks Additional support for
From playlist Explainers
Nicolás Matte Bon: Confined subgroups and high transitivity
A subgroup of a group is confined if the closure of its conjugacy class in the Chabauty space does not contain the trivial subgroup. Such subgroups arise naturally as stabilisers for non-free actions on compact spaces. I will explain a result establishing a relation between the confined su
From playlist Dynamical Systems and Ordinary Differential Equations
Stefaan Vaes: "Outer actions of amenable groups on von Neumann algebras"
Actions of Tensor Categories on C*-algebras 2021 Mini Course: "Outer actions of amenable groups on von Neumann algebras" Stefaan Vaes - KU Leuven Abstract: I will give a survey lecture on the classification of outer actions of amenable groups on von Neumann algebras with the main focus b
From playlist Actions of Tensor Categories on C*-algebras 2021
Acylindrically hyperbolic structures on groups - Balasubramanya
Women and Mathematics Title: Acylindrically hyperbolic structures on groups Speaker: Sahana Hassan Balasubramanya Affiliation: Vanderbilt University Date: May 23, 2017 For more videos, please visit http://video.ias.edu
From playlist Mathematics
Alex Margolis: Quasi-actions and almost normal subgroups
CIRM VIRTUAL EVENT Recorded during the meeting"Virtual Geometric Group Theory conference " the May 27, 2020 by the Centre International de Rencontres Mathématiques (Marseille, France) Filmmaker: Guillaume Hennenfent Find this video and other talks given by worldwide mathematicians on CIRM
From playlist VIRTUAL EVENT GEOMETRIC GROUP THEORY CONFERENCE
Alex Margolis: Quasi-actions and almost normal subgroups
CIRM VIRTUAL EVENT Recorded during the meeting"Virtual Geometric Group Theory conference " the May 27, 2020 by the Centre International de Rencontres Mathématiques (Marseille, France) Filmmaker: Guillaume Hennenfent Find this video and other talks given by worldwide mathematicians on CIRM
From playlist Virtual Conference
Stefaan Vaes, Superrigidity for dense subgroups of Lie groups and their actions on homogeneous space
Noncommutative Geometry Seminar (Europe), Oct. 6, 2021
From playlist Global Noncommutative Geometry Seminar (Europe)
Visual Group Theory, Lecture 1.6: The formal definition of a group
Visual Group Theory, Lecture 1.6: The formal definition of a group At last, after five lectures of building up our intuition of groups and numerous examples, we are ready to present the formal definition of a group. We conclude by proving several basic properties that are not built into t
From playlist Visual Group Theory